Multiple position wall switches for controlling a load, such as fan speed, are known in the art. Typically, the switch includes control circuitry responsive to each setting thereof to control the power delivered to the load. For example, U.S. Pat. No. 4,408,150 discloses a so-called "quiet" fan speed control that provides several selectable impedances, typically capacitors in series with the motor armature of the fan, to provide various reduced levels of power to the motor from an AC source. The power reduction is proportional to the series impedance. Switches of this type are said to be "quiet" since they do not use semiconductor switching techniques, and therefore do not produce audible high frequency noise. Another example is the De-Hummer Fan Speed Control manufactured by Power Controls of San Antonio, Tex. This device is wall mountable and is operated by a rotatable switch and actuator. The switch can be positioned to select among four capacitance values, thus providing four discrete speed settings and an off setting.
A drawback of rotatable switches is that they do not provide a quickly discernable indication of their setting, since the rotation has no inherent starting or ending point. Linearly actuable switches overcome this drawback, since the speed setting can be visually determined by the position of the slider or actuator.
Conventional linearly actuated switches are designed to be operated by one or two fingers moving relative to a hand that is fixed within a local frame of reference. They are not well-adapted for wall mounted use, where the entire arm may be used to actuate the switch. Specifically, the force required to move the switch from one position to the next typically results in overshoot, due to the feedback control characteristics of the human arm/muscle system, which quickly pushes the actuator past the desired position. This makes wall mounted linear switches of this type difficult to use.
The Sunrise Whispurr fan speed control manufactured by Lightolier Controls, Secaucus, N.J., includes a four position linear slide switch for selecting among three speed settings, and an off setting. The actuator requires application of a relatively large force (between about 1.5 and 2 lbs.) to move it from one position to the next. In addition, the actuator can be inadvertantly set between adjacent positions so that the switch becomes inoperative and power is removed from the fan motor.
Co-pending, commonly assigned U.S. patent application Ser. No. 478,604 filed Feb. 12, 1990 discloses a quiet fan speed control with a linear adjustment actuator. The switch disclosed in that application employs a slidable actuator having a pair of cantilevered members that cooperate with a cam surface having sloped walls that define a series of detention steps. As the actuator is moved from one position to another, the cantilevered members flex inwardly and outwardly, and at each detention step, engage a notch so as to provide tactile feedback to a user that the actuator has been moved from a position corresponding to one setting to another. As a result of the structure of the switch disclosed therein, the "force profile", i.e., the amount of force required to displace the actuator from one position to another, is both linear and abrupt.
FIGS. 1 and 2 hereto illustrate mechanisms 10, 10' which have been used in prior art multiple position linear slide switches. As shown in FIG. 1, the mechanism 10 comprises a board 12, such as a circuit board, having an actuator 22 disposed thereover. The board 12 has a plurality of pairs of contacts 24 disposed thereon, each defining a different setting of the switch. Disposed on the underside of the actuator 22 is a conductor 18 biased against the contacts 24 by springs (not shown). A ball 16 cooperates with one of a plurality of detents 14 disposed between each pair of contacts 24. When the actuator 22 of switch 10 has been moved to a position corresponding to one of the settings, a spring 20 urges the ball 16 into a corresponding one of the detents 14, and the conductor 18 provides an electrical connection between a pair of the contacts 24. The mechanism 10' illustrated in FIG. 2 operates in substantially the same manner, except that the spring 20' urges the ball 16' into one of a plurality of detents 14' located on the other side of the actuator.
A drawback of both mechanisms is that the conductor 18 (18') which travels with the actuator 22 (22') drags on the contacts 24 (24') as the actuator 22 (22') is moved from one position to another. Another drawback is that the construction of mechanisms of this type can make their assembly time-consuming and/or difficult since the ball 16 must be maintained in alignment with the spring 20 as it is compressed, and there is nothing to keep the ball 16 from becoming dislodged until it has been captured between the actuator 22 and the board 12.
U.S. Pat. No. 4,152,565 discloses a BCD slide switch that employs a pair of balls compressed between curved cam surfaces and into the sides of an actuator (rather than underneath or on top of the actuator, as in FIGS. 1 and 2 above). As in the case of FIGS. 1 and 2 above, a conductor is employed to establish electrical connection between contacts as the actuator is moved from one position to another. This switch, however, suffers from the same drawbacks as those described in connection with U.S. application Ser. No. 478,604 and FIGS. 1 and 2 described above. That is, the conductor drags on the contacts as the actuator is moved from position to another, and assembly of the switch may be difficult and/or time consuming since the balls 32 must be compressed into the actuator 6 while locating it between the cam surfaces to prevent them from becoming dislodged during assembly. Moreover, the switch of U.S. Pat. No. '565 is not suitable for wall mounting, nor is the structure disclosed therein suitable for carrying the high load currents frequently carried by wall mounted switches.
It is therefore desirable to provide a wall mountable, multiple position control switch with a linear adjustment actuator that has smooth positive operation between positions without overshoot while providing tactile feedback to the user. It is further desirable that such switch be simple in construction and therefore easy to assemble. The switch of the present invention achieves these goals.